So you want a mapping like this (top to bottom row):
(([: , [: |. |:),:~[:,]) ,&.>/~ i. 3
+---+---+---+---+---+---+---+---+---+
|0 0|0 1|0 2|1 0|1 1|1 2|2 0|2 1|2 2|
+---+---+---+---+---+---+---+---+---+
|0 2|1 2|2 2|0 1|1 1|2 1|0 0|1 0|2 0|
+---+---+---+---+---+---+---+---+---+
For any starting coordinate,
fliptp2D=: 4 : '({:y),x-{.y'
So,
2 fliptp2D &.> ,,&.>/~ i. 3
+---+---+---+---+---+---+---+---+---+
|0 2|1 2|2 2|0 1|1 1|2 1|0 0|1 0|2 0|
+---+---+---+---+---+---+---+---+---+
where the left argument is the row max.
On Mon, Jan 28, 2013 at 3:10 PM, Brian Schott <[email protected]>wrote:
> Raul,
>
> If I have translated your code correctly, then I don't think it
> produces the correct results.
>
> rtf =: monad define NB. Raul's transpose flip
> n=. %:#y
> r=. y
> for_j. i. n do.
> for_k. i. n do.
> i1=. j+n*k
> i2=. j*n-(1+k)
> if. i1 < i2 do.
> t=.i1{r
> r=.(i2{r) i1}r
> r=.t i2}r
> end.
> end.
> end.
> r
> )
> rtf i. 9
> 0 2 4 3 1 5 6 7 8
>
> By efficiency I mean that minimizing swapping stuff. But that may not
> be a good efficiency, I suppose.
>
>
> On Mon, Jan 28, 2013 at 2:41 PM, Raul Miller <[email protected]>
> wrote:
> > On Mon, Jan 28, 2013 at 2:34 PM, Brian Schott <[email protected]>
> wrote:
> >> I realize there are approaches like Raul and Devon are proposing that
> >> use 2D array indexing and require two array resequencing, but I was
> >> hoping to do both steps at once arithmetically to resequence the
> >> single index list to achieve efficiency.
> >
> > What do you mean by efficiency?
> >
> > Time?
> >
> > Space?
> >
> > Code?
> >
> > Forum? (But I'll stop trying to move this to chat, I guess...)
> >
> > Anyways, here's an in-place implementation:
> >
> > int * whatever(int n, int * r) {
> > for (int j= 0; j < n; j++)
> > for (int k= 0; k < n; k++) {
> > int i1= j+n*k;
> > int i2= j*n-(1+k);
> > if (i1 < i2) {
> > int t= r[i1];
> > r[i1]= r[i2];
> > r[i2]= t;
> > }
> > }
> > return r;
> > }
> >
> > --
> > Raul
>
> --
> (B=)
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
--
Devon McCormick, CFA
^me^ at acm.
org is my
preferred e-mail
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